Electric space discharge circuits



Jan. 20, 1948. F, KRQGER 2,434,704

ELECTRIC SPA CE DISCHARGE CIRCUIT v Filed March 20, 1944 3 Sheets-Sheet l sue -a sol/Res 0F Mom Mme VOL 71465 70 UT/L/ZAT/OA/ CIRCUIT INVENTOR FRED H. KROGER ATTORNEY Jan. 20, 1948. H, KROGER 2,434,704

ELECTRIC SPACE DISCHARGE CIRCUIT Filed March 20, 1944 s Sheets-Sheet 2 70 SOURCE OF MODULAT/A/G M VOLT/J65 }70LOA0 PHASE 11400014750 OUTPUT 70 80 m; 0F MODULATlA/G ou/:05 ml 3 A 1 v r0 0,110 I 23 JdMPL/TUDE MOOULATFD ourpur 'NVENmR FRED KRO ER ATTORNEY Jan. 20, 1948. I KRQGER 2,434,704-

ELECTRIC SPACE DISCHARGE CIRCUIT Filed March 20, 1944 3 Sheets-Sheet 3 I I I I ATTORNEY Patented Jan. 20, 1948 ELECTRIC SPACE DISCHARGE CIRCUITS Fred H; Kroger, Los 'AngelesgCalif assignor to Radio Corporation of America; a corporation of Delaware Application March'ZO, 1944, Serial No.--527,278

46 Claims. 1

and an= amplitude-modulator, although it will be 1 understood that-the-invention is not limited thereto:--

Inthe conventional-design of electron oscillatorsit has been necessary. to employ auxiliary circuitsincluding additional electron devices where it-is desired-to-maintain a constant average variable frequency and modulate the generated.

frequency-imaccordance with a variable control voltage. The use of these-auxiliary circuits in such-known arrangements not only unduly complicates-the entire system but also decreases the efiiciencypf-the system. Further, the cost of such a conventional-system is increased by the use of auxiliary circuits necessary to accomplish the foregoing desired result,

The presen-tinvention, among other things, overcomes-the disadvantages mentioned above by providing-an oscillation generator composed of asingle electron discharge device which maintains aconstant average value of frequency and is also capable--01? havingthe frequency directly modulated-in=accordance-witha variable control voltage, The=controlling energy required to frequency'modulate-my improved electron oscillator is verysmal-lh Oneof the objects of the present invention is to'provide arrefficient means of varying the relative-phase relation of the input and output of anelectron discharge device-at frequencies ranging.

from zero into megacycles.

Anotherobject of the present invention isto provide anein'cient control of the frequency of oscillations ofanelectronic oscillator by controlling the transit-time oithe electron stream.

A -further object is to provide a regenerative electronic device having means capable of varying the regeneration'at a frequency range from zero into megacycles.

Briefly, the foregoing objects of the present in vention and .others are achieved by employing.

electron discharge devices having a stream of electrons which require an appreciable interval of time for transit, and providing means for controlling the transit time through variation of the accelerating voltage. It is preferred to employ an electron tube having a-cathode, a collector electrode, one or more intermediate accelerating electrodes, and a suitable tank circuit. In one Darticular embodiment successfully tried out in practice, and described hereinafterfl employ an evacuated electromdischarge device of the beam type tubeh'aving a cathode atoneend, a collectorat the other end, a pair of intermediate accelerating electrodes, and an associated'cavityresonator for the output, the latter being external of the vacuum tube structure and having a gap across which the electrons pass for inductively exciting the tank, This tank circuit is in the form of a sur face of revolution with the central plane of the surface of revolution cutting the axis of the vacuum tube structure substantially at right angles. In its preferred form, the surface of revolution constituting the tank circuit is a section approximating the sector of a circle with the vertex angle located adjacent the vacuum tube-involved. Gen

eral-ly speaking-,-such structure may be'said to be doughnut in form; For focussing the electrons there is provided'a'pairof magnetic lenses each constituted by a leakage field surrounding the envelope ofa vacuum tube. Such a vacuum tube and-associatedtank circuit is generally disclosed in my application Serial No. 296.045,'filed September 22, 1939, now United States Patent No. 2 350,907, "granted June 6;"1944', to which reference is herein made. It should-be understood, how ever, that this typeof tube and tank circuitis merely given by way of illustration since the principles of the invention are equallyapplicable to any other beam type tube which can be used for my purposes. It should also be'understood that other types of tank circuits can be used, asforexample a concentric line tank.

In accordance with one embodiment of the invention relating to an oscillator circuit, in order to obtain regeneration there is provided a feed back circuit between the output and the input, and meansare provided for varying the potential on the accelerating"electrodes of the tubes in order to affect the transit time of the electron stream. Thus by varying the accelerator ele'c-' trode 'potential,I am able to vary the velocity of the electrons in the electron stream through the tube and thus vary the phase relation between the output and inputcurrents. Consequently, as the relative'phase'of'the currents fed back from the output circuit to the input circuit is changed, the operating frequency is changed to a value which will bring the regenerative voltage in phase with the tank voltage. The sensitiveness of the oscillator frequency to accelerator potential change may be increased by lengthening the distance from the control electrode to the output gap of the tank circuit or by employing lower potentials and lower electron velocities. Further, this sensitiveness may also be increased by employing less sel ctive oscillator circuits.

The vacuum tube of the present invention, when employed as an oscillator, finds a wide field of use in wide band frequency modulation. When used for this purpose, the frequency change of the oscillator may be made to be substantially proportional to the potential change for a small range with a small change in amplitude of the output from the oscillator. For a wider frequency range, suitable compensating circuits may be employed to make the frequency change substantially proportional to the potential change, also with a small change in amplitude over this range. Of course, where an accessory amplitude limiter is employed with the oscillator of the present invention, this limiter will replace the amplitude compensator circuits and obviously the amplitude of output of the system will be constant over any desired range of frequencies.

A brief discussion of the principles underlying the oscillator embodiment of the invention follows: It is known that in an electron oscillator where oscillations are the result of an amplifier feeding back suflicient energy to the control element to exceed the losses, the energy fed back from the output to the input or control element must bein correct phase to maintain oscillations. In an electron device of the beam tyne with which the present invention is primarily concerned. the transit time of the electrons is appreciable. and the following factors enter into a determination of the frequency of oscillation.

(a) The constants of the tuned output circuit involving L, C and P which respectively refer to the inductance. the capacitance and the power factor reciprocal of Q.

(b) The transit time of electrons.

(c) The constants of the tuned input and feed back circuit, here again involving L, C and P.

The frequency of the oscillator can be varied by varying either one or more of the factors (a), (b) or (c). The varying of the L, C or P for modulation purposes over the frequency range of zero into megacycles in order to achieve one of the results of the present invention has been found in practice to be difiicult. Varying the transit time in accordance with the invention achieves the desired result in a much simpler and more efficient manner. Since this transit time is determined by the length of the electron path and the voltage accelerating the electrons, it is proposed, in accordance with the invention, to vary the electron velocity and thus change the transit time by varying the accelerating voltage in accordance with any desired type of signal modulation. By increasing the accelerator voltage by a given amount, the transit time is decreased according to the law that the electron velocity is proportional to the square root of the voltageapplied to the accelerator electrode. In order to obtain a maximum change in frequency for a given change in moduation voltage, it is desired, in accordance with the invention, to have a minimum resultant change in phase in the input and feed back tuned circuits for a given change in frequency, and for this reason the Q of the input and feed back circuits (reciprocal of power factor) is made as low as practical and the Q of the output resonator (tank circuit) is reduced to a value which will give the desired frequency change.

Another embodiment of the invention comprises a phase modulator which differs from the frequency modulator described above in that the feed back circuit is absent and a source of constant frequency oscillations is supplied to the control element.

Another embodiment of the invention comprises an amplitude modulator in the form of a regenerative repeater. This modulator employs the feed back feature present in the frequency modulator embodiment of the present invention and requires the application of a source of constant frequency oscillations to the control element.

A more detailed description of the invention follows, accompanied by a drawing wherein:

Fig. 1 illustrates a variable frequency oscillator or frequency modulator in accordance with one embodiment of the invention;

Fig. 2 illustrates a phase modulator in accordance with another embodiment of the invention;

Fig. 3 illustrates an amplitude modulator in accordance with a still further embodiment of the invention; and

Fig. 4 illustrates another embodiment of the invention in the form of a variable frequency oscillator or frequency modulator.

Referring to Fig. 1 in more detail, there is shown an electron discharge device oscillator circuit comprising a vacuum tube structure (generally of the so-called inductive output type) consisting of an evacuated glass envelope l containing within it a cathode 2, a heater 3, a grid 4, ring-like accelerator electrodes 5, 5 and collector electrode 5 and a suppressor 1. The heater 3 is supplied with energy from a suitable alternating current source, as shown, through choke coils 8. Connected to the cathode 2 and grid 4 is the input tuning circuit 9, which includes a variable condenser iii. The collector electrode 6 for gathering the electrons traversing the length of the glass envelope l is shown to be cup-shapedin form, although, if desired, it may be hemispherical, conical or of other suitable shape. Centrally located within the interior of the collector 6 there is provided a rod-like suppressor electrode '5 for gathering secondary electrons which may emanate from 6. The suppressor electrode 1 may take any suitable form according to the design of the collector electrode 6. Accelerator electrodes 5, 5 are narrow in width, and are connected together and connected to a suitable source of modulating voltage 30. Condenser 3| is a bypass condenser to ground. Source of modulating voltage 3%) may comprise speech waves, any suitable variable frequency, a space wave keying system, or an on-ofi keying system.

Surrounding the exterior of the glass envelope I and located intermediate the two accelerator lane I. *Imorder' to obtainta desired-high imped ance across the gap a, b of the .tankcircuit .ior matching -the impedance. of the .wacuum ,tube structure, the configuration of tankcircuit al 2,. as

shown by l a cross-section of. thesurface =f-.revolution through the axisof revolutionin the .plane .of.-.the. drawing, should approximate two. equal sectors with their. vertices: toward the .glass en- .velopel. ..The dimensionof the tanker resonant cavity. circuit 1 Zasmeasured fromgthe centerof theeglass. envelope I: toward the-eraser. the. .sec- -tor,. as.indicated in .thedrawing; is. approximately one-quarter of the. lengthof :thetcommunication wavescorresponding to the resonant" frequency, provided that. the .gap a,'-.b. isnot. supplied; with capacitor; discs tochange :thefrequency. toayalue less than thenatural frequency or-the resonator. The tank circuit 2 .-is preferably made, of. ahighly electrical .conductingmaterial, .such as copper.

rzForcfocusing. :the electron beam :there are, providedsaepairof magneticlenses, in. series relation constituted by gaps c, d and e, f formedby. spaced ironsleeves l4, l5 and; .ifiwh-ich surround the glass envelope I and are-. serially arr-angedqwith respect toan iron magnetic path. This ;mag-

.netic path includes, a strip of iron I l, whichds placed; adjacent to the sides 1 of the upper sector ofxthe tank. 12 andiwhichisqcompleted through aniron core l8,vin-,.turn surrounded by an.el ectromagnetic ,field coil-or-solenoid; i!9-- excited by a direct current source of supply 20.

In .order :to sustain-oscillations,jthe outpl t coupling coil- 2 l. .is hereyshown coupled -.b acl to: the tunediinput circuitfi through afeed backtransmission:1ine=23,---which line, is. adjustable in electrical length by means of trombone sliders 24, Z LuA Lecher wire system 2515 connected to the output coupling: coil 2 I. and one end of; the transmission line; 23 is slidablytconnected to; this Lecher wire system, as. shown, while theother end is inductively-coupled to the. input circuit 9. .Aslider- 26 bridgedacrossqthe conductors ofthe Lecher wire system c 25 functions to tune the ,output circuit.

The operation of the oscillator-will now be given. The grid bias on. electrode i is produced by the conventional gridleak: 1 3. 'The i accelerator electrodes 5, 5 ,are maintained at a-giyen positive bias. "The electrons immediately j after passing through the apertures. ofrsridtwill tend .to flow toward the interior; surface of? the; first accelerator electrodeq5 .dueto the positive jpotentialpn this electrode. In order to prevent the electr s a r m .impin ingc t i acce er o e e trode there is provided amag netic lens-p; d which, byvirtueof t e leaka e. fie thercacrcss theme the electrons tow r the.ax s;or he-va uum ube- As thec ect nsanprca h. h can a .themis tendency toward dispersion, and i is for; this reason thatthe additional-magnetic; ns e, f is requiredto maintain the beamin th I is fthe tu e b nd the cqn acce retp set -Whic the electrons will be gathered up by the collector electrode 6 which is at a suitable positive potenlre at eto esethcde th ows of-w lcc rc .or puls ;t rme vveridee ciiciic. feed, ackcircuit; t avers the-re end;..- du -hi h irs sne -r. urrcntsgbetwecntih oint a, b.

Th vol a e induce a e sancfi f the resonator l2 will in. turn induce ,a current in. the resonator which through the outputcouplingloop 2i causesa resultant feedback through the transmission line 23 andstheinput circuit-9, In. to the .grid 1 4. :Ifthis feed-'- back issufilcient to overcome zthe rlosses, oscillations will resultm due l lin The :frequency ,of the oscillations will be such. as tocause the? feed; back voltage to beef aphase that will augment the energyin theresonator 12. qThe'. establishment of this correct phasewill be. effectediby; an automatic adjustment of transit ttimeuandephase relations of resonator and feede back circuits. This frequency of oscilla- ,tion,..-when;there isnoi-moduation, will represent the mean val lfi of carrier frequency. When there ismfld llationrvoltage; applied by source 30, there will be; 911. 11; an increase or a decrease of accelerator-woltage, depending upon the modulation. 'I his variation i111 the modulating voltage and; consequent; variation in the accelerator -yolt- Q Wh lf1;; in; turn will affiectthe transit time;of the electrons the stream, will change the phase .of-the ieed backenergy proportionately. This change in;ph ase w ill cause a change in the frequency:ofoscillationsdue to the inherent tendency- 0f an; oscillator to maintain-proper phase relation; between feed-back and induced voltage.

In ,practi ee, the Q of the input circuit 9, H], as well; as the transmission line 23 and thecoupling loep 2|, zliyisrnade as low as practicable so that the-phaseshift therein will be a minimum fora given change-infrequency, and the Q of theresonator l2 is chosen-for the particular deviation in; -fr equencyrequired. The dimensions and position pf loop-H are adjusted so that the efiectiveQof. the-resonator is low enough to accommodatethep frequency deviation desired. As a practical matter, each time the feed back or load .co plingis changedit may be necessary to adjust-the-tuning of the output circuit. Another means for adjusting the efiective Q of the resonator is by adjusting the positions of the taps (an-line: 25 extending to the utilization circuit. Any-lessrvalue of Q for the resonator will result in an undesirable and unnecessary decrease in .efilciency. In; practice, it. is desired that the Q of the-resonator be sufficiently low to permit frequency modulation over a desired range. of frequencies withrelatively. small changes in amplitude-over. said range. If desired, the loop 2| may bereplacedby ai ly-suitable coupling element or elements, such asan open dipole, whose dimensionsandposition also control the effective Qof the resonator.-

'In oneembodimfintactually tried out in-practicer theayerage frequency or carrier was-480 megacycles and the oscillator was varied over a range. of plus and :minus 2 /2 megacycles about this -mean frequency of 480 megacycles. The .averagevoltage applied to the accelerating electrpdesiwas. 2500 volts positive, and the voltage applied to the collector .electrode was 1200 volts positive. ..Although these values of voltage were .employed in @connection with an experimental model successfully constructed to demonstrate the principles involved, it should be distinctly understood that these. values are merely illustrative ,and, thataselectron tubes become commercially ayailable and thetransit time and relative distances vcf the electrodes, are changed from those reme ed-durin the d mo tra io that o ,llseiu re ueswi l esu t- I he phase modulator and amplitude modulating embodiments shown in Figs. 2 and 3 respectively, have been considerably simplified in order to show only the essential elements of the tube structure necessary for an understanding of the principles involved. The electron focusing elements and the envelope of the vacuum tube have not been shown in Figs. 2 and 3-in order to simplify the drawing. -Those-elements of these figures which are the same or equivalent to the elements shown in Fig. 1 are represented by the same reference numerals.

In Fig. 2 there is shown a constant source of high frequency currents 32 for applying between the cathode 2 and grid t a voltage to modulate the density of the beam of electrons emanating from the cathode. This beam of electrons which is modulated by the high frequency wave impressed by source 32 on the grid 4 tranverses the gape, b of the resonator I2 before impinging on the positively charged collector electrode 6, and excites the resonator l2 by induction in the manner now known in the art. The accelerator electrodes 5, 5 are connected together and coupled to a suitable source of modulating voltage 30, the latter impressing the alternating current voltage upon the electrodes 5, 5 for causing either an increase or decrease of the accelerator voltage depending upon the modulation. As in the case of Fig. 1 described above, this variation of modulating voltage with the consequent variation in the accelerator voltage will affect the transit time of the electrons in the stream and thus change the relative phase of the input voltage on grid 4 with respect to the induced voltage in the resonator. Coupling loop 2| is used to derive an output current whose phase continuously varies in accordance with the modulating voltage. Since it is desired to have as little amplitude modulation as possible over the desired range of frequencies, the Q of the resonator l2 should be reduced to the lowest practical value. This reduction of the Q of the resonator is predicated upon not having an amplitude limiter stage following this phase modulator.

Fig. 3 shows an amplitude modulated system employing a regenerative feed back circuit 23' extending from the output loop 2| back to the input circuit 2, 4. Here again there is provided the constant source of high frequency waves 32 for exciting the grid 4. In the operation of this circuit the regeneration adjustment is set to prevent oscillations within the range of modulation. The increase or decrease of the accelerator voltage on the electrodes 5. 5 caused by the application of modulating voltage from 30 will cause a change in the phase between the voltage on grid 4 and the voltage induced in the resonator l2. This phase change in turn causes a corresponding change in the regeneration resulting in a variation in the amplitude of the output voltage. In order to have a minimum phase modulation coincident with amplitude modulation, a highQ is chosen for the resonator l2. This Will'in turn ive high efiiciency. The Q of the feed back circuit 23' may be any value that is convenient.

In the operation of the circuit of Figs. 1, 2 and 3, the velocity of the electrons in the stream throughout the length of the beam (the useful part of the stream) is substantially constant, except for such deceleration as is caused by the energy taken by the resonator l2. The same potentials on both accelerator electrodes 5, 5 insures this desired constant velocity condition. There is a minimum electric field in the beam in the space between the accelerator electrodes (substantially electric field free space), and it can be said, in eiTect, that the electric field of the tank 12 is superimposed on this minimum field in order to decelerate the electrons. The particular embodiments of the invention shown herein make no use of velocity modulation, as is commonly known in the art, for the purpose of obtaining high frequency feed back by grouping or bunching the electrons.

In the design of the electron discharge device circuits of Figs. 1, 2 and 3, it may be advisable to operate the system with the resonator l2 at the same average potential as the accelerator electrodes 5, 5. This is done in order to prevent any potential gradients affecting th electron beam between the two accelerator electrodes 5, 5. Where a single ended circuit constituting a coaxial line is employed for an input or an output circuit, it is necessary to prevent the application of the direct current voltage on the resonator to the grounded outer conductor, and a condenser is used for this purpose. This condenser is made to have low impedance to radio frequency current in order to by-pass the same to ground. Since the accelerator electrodes are subjected to a modulation potential, the resonator in this instance would be isolated from these electrodes by a choke and/or resistor effective for the modulation frequencies,

Fig. 4 shows the principles of the invention applied to a frequency modulated transmitter. This figure is identical with Fig. 1, except for the following features: (1) Fig. 4 employs only one accelerator electrode 5, and (2) the cavity resonator I2 is maintained at the same average potential as the accelerator electrode. The efiective Q of cavity i2 is adjusted by adjusting the dimensions and location of loop 2|, or by adjustment of the load taps on line 25, to be sufiiciently low so that frequency modulation is obtained over a desired range of frequencies with relatively little change in amplitude over these same frequencies.

It should be understood that the invention is not limited to the precise embodiments shown in the drawing and described in the specification, since various modifications may be made with out departing from the spirit and scope of the invention. As an illustration, the principles of the invention are applicable to a regenerative amplifier where it is desired to change the degree of regeneration at any frequency varying from zero into the range of megacycles. Further, the output coupling loop 2| can be replaced by any suitable coupling arrangement, either capacitive, inductive or conductive. Moreover, the result of the invention can be obtained by modulating only the accelerator adjacent the cathode, as Well as by modulating both accelerators. It will thus be obvious that it is possible to design the tube in which there is only present the accelerator adjacent to the cathode. The number of accelerator electrodes used in addition to the one adjacent to the cathode depends upon the refinement of the tube design.

The term angular velocity used in the appended claims is deemed to include both frequency modulation and phase modulation phenomena.

What is claimed is:

1. In an electron discharge device having a pair of electrodes between which an electron stream passes, and a single tuned circuit physically located between said pair of electrodes and in energy coupling relation to said stream, the method of operation which includes biasing said pair of electrodes positively and to the same degree, and varying said bias in accordance with a continuously variable frequency wave, whereby the time of transit of the electrons in the space between said electrodes is varied with a consequent continuous change in the relative ph Of" the Voltage induced 1 in; said, tune d, cira su 1 2. In an electron beam tubehaving a" cathode,

.;an input; electrode having a voltage impressed rthereomzand'asingle output tank circuit adapted to be excited inductively by the passage of a stream of electrons emanatingfromsaid cathode, and an electron accelerator electrode. positioned between said input electrode and said output tank ,and maintained at a positive direct current po tential relative to said cathode, the method. of

operation which includes varying the efiective ,bias potential on said accelerator electrode in a continuous manner inaccordance'with a variable audio frequency wave to thereby vary thetime of transit of electrons insaid stream and the phase relation between the input voltage .andthe induced voltage in the tank.

3. In .an electron beam regenerative tube .having a cathode, a control electrode, a source of constant frequency oscillations coupled between said control electrode and cathode, an output .circuit adapted to be-excited inductively by the ,.,passage of a stream of electrons-emanating from .said. cathode, and a feed. back circuit between ,,said output circuit andsaid control electrode,

the method of operation whichincludes varying .thephase relationbetween the voltage induced in saidoutput circuit and the voltage, fed back to said control electrode, by varying the transit time.

,of the electrons insaid stream.

4. Inan electron dischargedevice modulation system including asource ofsignalmodulations and apair of electrodes between which an electron streampasses, a directconnection of substantially zero impedance for. all modulating irequencie coupling said pair of electrodes together,

a. tank circuit having a gap locatedbetween said pair of electrodes and across whichgap said electron stream passes, said tank being arranged to be inductively excited by the passage of the e1ectrons across said gap, the method ofoperation which includes varying thejdensity of the. elec trons in said stream prior to the passage of said electrons past the first ofsaid pair of electrodes, and varying in accordance with signal modulations the electron transit time between said pair of electrodes.

,5. In an electron discharge device modulation system including a source of signal modulations and a pair ofelectrodes between which an electron stream passes, a direct connection of substantially zero impedance for all modulating frequencies coupling said pair of electrodes together,

; quency rate prior to the passage of said electrons past the first of said pair of electrodes, and

varying in accordance with signal modulations the electron transit time between said pairof electrodes.

6. An electron discharge device circuit including means for projecting a stream of electrons, a-tuned circuit adapted to be excited by thepassage of the electrons in said stream and having a gap adjacent the stream of electrons whereby said tuned circuit absorbs energy from said stream, accelerating electrodes located on both ,Sides of said gapand maintainedat the same ,positive potential and means for. varying the voltage on said accelerator electrodes between certain limits, in accordance ..with, an undulatory -,wave, whereby. the transit time of the electrons in saidstream is caused to change.

7.. An electrondischarge device circuit. including a tank circuit in the form of asurface of revolution having a gap, asource of electrons ,for ,ppr-ojecting astream of electrons across saidgap forinducing a voltage. insaid tank circuit, acceleratingelectrodes located on both sides of said gap and maintained at a positive, potential relartive-to said source, and to the same. degree,, and

,means for.varyingthevoltageonsaid accelerator electrodes between certain limits in accordance causedto change.

, 8. ,An;electron discharge device circuit includin a tank circuit inthe form of a surface of rev- .olution-having a gap in the center thereoia cathode for projecting a streamof electrons across sadgap at rightangles to the central plane of..said surface for exciting said tank circuit, focussing means for said electrons,. accelerator electrodes on both sides of said gap, a source of unidirectional potential .for maintaining. said accelerator electrodes at a-positive potential rel- ,ativetosaid cathode and to the same degree, a source of alternating current having arange of .modulating. frequencies and connected .tosaid accelerator. electrodes whereby the potential ,on said accelerator-electrodes is varied in accordance ,Wlth the modulation witha consequentchange in the.transit time of the electrons in said stream.

9. An electron discharge device having ,a cathode, ,and a:pair of spaced positively biasedelecztrodes, saidpositively biasedelectrodes being separatedsolely by etheric space and maintained at the same positive potential, a tank circuit having an aperturelocated between said.electrodes. .and adapted. to be. excited, by the passage of electrons through said aperture, a connection between, said positively biased electrodes, means for directing electrons ifrom said cathode .past. said positively v.biasedelectrodes in succession with a velocity which issubstantially constant throughout. the distance between said positively biasedv electrodes, and a connection from said positively biased electrodesto a source of variablewave modulating voltage, whereby the transit. time of the ,electrons varies in accordancewith variation ofsaid modulating voltage.

10. An electron discharge device circuit includingatank circuit in the form ofa surface of rev- .olutionhaving agap, asource. of-electronsfor projecting a stream ofelectrons across saidgap .for inducing-awoltage, in said tank circuit, accellating electrodes located on both sides of said gap and maintained at the same positive potential, a control element located between said source of electrons and the first of said acceleratonelectrodes, a constant source of high frequency oscillations connected, between said. control. element and said source of electrons, ,andmeans forvaryingthevoltage on said accelerator electrodes in accordance with signal modulation whereby the transit time of the electrons in said streamis caused to change.

'11. An electron discharge devicecircuit including a tank circuit in the form of a surface of'rev- .olution having a gap, a source of electrons for projecting a stream of electrons across said. gap for inducing a voltage in said tank circuit, accelerating electrodes located on both sides of said .gap and maintained at the same positive potential, a control element located between said source of electrons and the first of said accelerator electrodes, a constant source of high frequency oscillations connected between said control element and said source of electrons, a feed back circuit extending from said tank, circuit to said control element, and means for varying the voltage on the accelerating electrodes in accordance with signal modulations, whereby the transit time of the electrons in said stream is caused to change.

12. An electron discharge device circuitincluding a tank circuit in the form of a surface of revolution having a gap, a source of electrons for projecting a stream of electrons across said gap for inducing a voltage in said tank circuit, accelerating electrodes located on both sides of said gap and maintained at the same positive poten-. tial, a control element located between said source of electrons and the first of said accelerator electrodes, a feed back circuit extending from said tank circuit to said control element, and means for varying the voltage on said accelerator electrodes in accordance with signal modulation, whereby the transit time of the electrons in said stream is caused to change,

13. An electron discharge device circuit including means for projecting a stream of electrons, a tuned circuit adapted to be excited by the passage of the electrons in said stream and havin an element adjacent the stream of electrons, whereby said tuned circuit absorbs energy from said stream, accelerating electrodes located on both sides of said element and maintained at the same positive potential, a control electrode located between said means and the first of said accelerator electrodes, a feed back circuit extending from said tuned circuit to said control electrode, and a modulating source of variable frequency waves connected to said accelerating electrodes for varying the accelerator voltage in dependence upon the modulation, with a consequent variation in the transit time of the electrons.

14. A modulator system for use at very high frequencies comprising an electron discharge device circuit including means for projecting a stream of electrons, a tuned circuit adapted to be excited by the passage of the electrons in said stream and having an element adjacent the stream of electrons whereby said tuned circuit absorbs energy from said stream, accelerating electrodes located on both sides of said element and maintained at the same positive potential, a control electrode located between said means and the first of said accelerator electrodes, a feed back circuit extending from said tuned circuit to said control electrode, and a modulating source of variable frequency waves connected to said accelcrating electrodes for varying the accelerator voltage in dependence upon the modulation frequency.

15. Apparatus in accordance with claim 14, characterized in this that said system is a frequency modulation system.

16. An amplitude modulation system in accordance with claim 14, characterized in this that a constant source of high frequency oscillation is connected between said control electrode and said means for projecting a stream of electrons.

1'7. A phase modulator comprising an electron discharge device circuit including means for projecting a stream of electrons, a tuned circuit adapted to be excited by the passage of the electrons in said stream andhaving an element adjacent the stream of electrons whereby said tuned circuit absorbs energy from said stream, accelerating electrodes located on opposite sides of said element and maintained at the same positive potential, a control electrode located between said means and the first of said accelerator electrodes, a constant frequency source connected to said control electrode, and a source of modulating voltage coupled to said accelerating electrodes.

18. In an electron discharge device having a cathode, an input control electrode, and an output tank circuit adapted to be excited inductively by the passage of a stream of electrons emanating from said cathode, the method of operation which includes producing constant high frequency oscillations, impressing said constant frequency oscillations between said control electrode and said cathode, and subjecting the electrons between said control electrode and said tank to a varying electric field in accordance with signal modulations.

19. Inan electron discharge device having a cathode, an input control electrode, and an output tank circuit adapted to be excited inductively by the passage of a stream of electrons emanating from said cathode, the method of operation which includes impressing constant frequency oscillations between said control electrode and said cathode, also feeding back energy from said tank circuit to said control electrode, and subjecting the electrons between said control electrode and said tank to a varying electric field in accordance with signal modulations.

20. An electron discharge device circuit including means for projecting a modulated stream of electrons, a tuned circuit adapted to be excited by the passage of said modulated stream and having an aperture adjacent the stream of electrons whereby said tuned circuit absorbs energy from said stream, an accelerating electrode located between said aperture and said means, means for maintaining said accelerating electrode at a positive potential, and means for varying the potential on said accelerator electrode in accordance with variable frequency ignal modulations, whereby the transit time of the electrons in said stream is caused to change.

21. An electron discharge device circuit including a cathode for supplying a stream of electrons, a cavity resonator having a gap therein located in the path of travel of said electrons, whereby said stream of electrons and said resonator are in energy coupling relation, first and second electron permeable electrodes located between said gap and said cathode, a source of alternating current coupled to saidfirst electrode, a source of unidirectional potential for maintaining said second electrode at a positive potential relative to said cathode, and means for varying the potential on said second electrode in accordance with signal modulations, whereby the transit time of the electrons in saidstream is caused to change.

22. An electron discharge device circuit including a cathode for supplying a stream of electrons, a cavity resonator surrounding a portion of the path of travel of said stream, said resonator having aperture in both sides thereof to enable said electrons to pass through said resonator, whereby said stream of electrons and said resonator are in coupling relation to each other, first and second electron permeable electrodes located between said cathode and the first of the apertures of said resonator to ,be traversed by said electrons, a source of alternating 13 current coupled to said first electrode, a source of unidirectional potential for maintaining said second electrode at a positive potential relative to said cathode, and means for varying the potential on said second electrode in accordance with signal modulations, whereby the transit time ofthe electrons in said stream is caused to change.

23. An electron discharge device circuit including a cathode for supplying a stream of electrons, a cavity resonator surrounding a portion of the path of travel of said stream, said cavity resonator being in the form of a surface of revolution with the central plane thereof substantially at right angles to the path of travel of said stream, said resonator having apertures in both sides thereof to enable said electrons to pass through said resonator, whereby said stream of electrons and said resonator are in coupling relation to each other, first and second electron permeable electrodes located between said cathode and the first of the apertures of said resonator to be traversed by said electrons, means for impressing an alternating potential on said first electrode, a source of unidirectional potential for maintaining said second electrode at a positive potential relative to said cathode, and means for varying the potential on said second electrode in accordance with signal modulations, whereby the transit time of the electrons in said stream is caused to change.

24. In an electron beam tube having a cathode, an input electrode having a voltage impressed thereon; and a tuned circuit in inductive coupling relation to the stream of electrons emanating from said cathode, and an accelerator electrode positioned between said input circuit and said tuned circuit and maintained at a positive direct current potential, the method of operation which includes varying the eifective potential on said accelerator electrode in accordance with an audio frequency wave to thereby vary the time of transit of the electrons in said stream and the phase relation between the input voltage and the induced voltage in the tuned circuit.

25. In an evacuated electron discharge device circuit, means for supplying a stream of electrons, a cavity resonator surrounding a portion of the path of travel of said stream, said cavity resonator being in the form of a surface of revolution with the central plane thereof substantially at right angles to the path of travel of said stream, said resonator having apertures in both sides thereof to enable said electrons to pass through said resonator, whereby said stream of electrons and said resonator are in coupling relation to each other, an accelerating electrode located between said means and the first of the apertures of said resonator to be traversed by said electrons, means for maintaining said electrode at a positive potential relative to said electron supplying means, a source of speech waves coupled to said electrode for varying the potential on said electrode, whereby the transit time of the electrons in said stream is caused to change, a control grid located between said accelerating electrode and said first means, and a source of high frequency current coupled to said control grid.

26. In an electron discharge device oscillator system having a pair of electrodes between which an electron stream passes and a single tuned circuit physically located between said pair of electrodes and in energy coupling relation to said stream, the method of producing a high frequency carrier of a frequency determined over a certain band by'th amplitudaofa controlling voltage which includesbiasing said pair of elec-' trodespositively, and varying the relative phase of the voltage induced in said tuned circuit by simultaneously varying between certain limits and in'continuous manner the bias on said pair of electrodesin accordance with variablefrequency signal modulations.

27. In an electron discharge device'oscillator system having a pair of electrodes between which an electron stream passes and a tuned circuit located-between said pair of electrodes and in energy coupling relation to said stream, the

method of produ'cinga high frequency carrier of a frequency determined over a certain band-by the amplitude of a controlling voltage which includes'biasing saidpair of electrodes positively,

and varying the relative phase of the voltage induced 'insaid tuned circuit by simultaneously varying between certain limits and in continuous manner the" bias on said pair of electrodes in accordance with variablefrequency signal modula tions and to the same degree.

28. A phase modulator comprising an-electron discharge device circuit including means for projecting a stream of electrons, a tunedcircuit adapted to-be excited by the passage of the electrons in said stream and having an element adjacent the stream of electrons whereby said tuned circuit absorbs energy from said stream, accelerating electrodes located on both sides of said element and maintained at the same positive potential, a control electrode located between said means-and the first of said accelerator electrodes, a constant frequency source connected to said control electrode, and a source of variable frequency modulating voltage coupled' to said accelerating electrodes.

29. An electron dischargedevice'system for operation over'a range of frequencies comprising means for-projecting a stream of electrons, a cavity resonator of relatively low Q having a gap and adapted to be excited by the passage of electrons in said stream across said gap, an electron accelerator electrode positioned between said means and said resonator, a source of unidirectional potential for maintaining said accelerator electrode at a potential which is positive relative to said means, and means for varying the transit time of said electrons in accordance with signal voltages, a load coupled to said resonator by a coupling element in the interior of said resonator, the degree of coupling between said resonator and said load being such as to provide a desired effective Q of the resonator which permits modulation over said range of frequencies with relatively small change in amplitude.

30. An electron discharge device system for operation over a range of frequencies comprising an electron emitting cathode, a cavity resonator of relatively low Q' having a gap and adapted to be excited by the passage across said gap of electrons emitted by said cathode, an electron accelerator electrode positioned between said cathode and the gap of said resonator, an electron collector electrode on the side of said gap remote from said cathode, a source of unidirectional potential for maintaining said accelerator electrode at a potential which is positive relative to said means, and means for varying the transit time of said electrons in accordance with signal voltages, a load coupled to said resonator by a coupling element in the interior of said resonator, the degree of coupling between said resonator andsaid load being such as to provide a desired effective Q of the resonator which permits modulation over said range of frequencies with relatively small changes in amplitude, the Q of said coupling element being made relatively low so that the phase shift therein will be a minimum for a given change in frequency, the Q of said resonator being only sufficiently low to accommodate the frequency deviation desired.

31. A frequency modulation generating system comprising an electron discharge device circuit including an electron emitting cathode, a cavity resonator having a gap and adapted to be excited by the passage of electrons across said gap, an electron accelerator electrode positioned between said cathode and said gap, means for maintaining said accelerator electrode at a positive potential relative to said cathode, means for varying the transit time of the electrons in accordance with signal voltages, whereby frequency modulated Waves are generated, said resonator having a Q which is sufficiently low to permit frequency modulation over a desired frequency range with relatively small changes in amplitude over said range.

32. An angular Velocity system comprising an electron discharge device circuit including an electron emitting cathode, a cavity resonator having a gap and adapted to be excited by the passage across said gap of electrons emitted by said cathode, an electron accelerator electrode positioned between said cathode and gap, means for maintaining both said resonator and said accelerator at the same average potential relative to said cathode, means for varying the transit time of the electrons in accordance with signal voltages, whereby angular velocity modulated waves are generated, said resonator having a Q which is sufficiently low to permit angular velocity modulation over a desired range with relatively small changes in amplitude over said range.

33. An electron discharge device system comprising means for projecting a stream of electrons, a cavity resonator having a gap and adap ed to be excited by the passage of electrons in said stream across said gap, an electron accelerator electrode positioned between said means and said resonator, means for maintaining said accelerator electrode at a positive potential, means for varying the transit time of said electrons in accordance with signal voltages, a load coupled to said resonator by means of a coupling element in the interior of said resonator, the dimensions and position of said coupling element being such as to give a desired effective Q for said resonator, and means for varying the Q of said resonator.

34. A frequency modulation generatin system comprising an electron discharge device circuit inciudingan electron emitting cathode, a cavity resonator having a gap and adapted to be excited by the passage of electrons across said gap, an electron accelerator electrode positioned between said cathode and said gap, an electron permeable electrode positioned between said cathode and said accelerator electrode, means for maintaining said accelerator electrode at a positive potential relative to said cathode, meansfor varying the transit time of the electrons in accordance with signal voltages, whereby frequency modulated waves are generated, said resonator having a Q which is suiiiciently low to permit frequency modulation over a desired frequency range with relatively small changes in amplitude over said range, and a feed back circuit of relatively low 16 i Q from said cavity resonator to said electron permeable electrode.

35. High frequency apparatus comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said ap, said discharge system comprising cathode, a single control grid, accelerating and anode electrodes arranged in the order named, a circuit connected between said control grid and cathode for varying the electron flow from said cathode and across said gap in a manner so as to cause high frequency excitation of said cavity, a source of signal modulating voltages connected to said accelerating electrode and said cathode, so as to subject said accelerating electrode to a modulating potential with respect to said cathode, and an output circuit coupled to the space in said cavity resonator to enable the derivation therefrom of modulated high frequency oscillations.

36. Apparatus as defined in claim 35, characterized by the fact that a coupling circuit is provided coupling the space in said cavity to the control grid and the cathode electrodes of said system.

37. Apparatus for producing frequency modulated waves comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said gap, said system comprising cathode, a single control grid, accelerating and anode electrodes arranged in the order named, a circuit coupling said cavity resonator to the control grid and cathode of said system, a circuit for suitably polarizing said anode with respect to said cathode, a circuit connected to said accelerating electrode and cathode fOr subjecting said accelerating electrode to a variable voltage with respect to said cathode so as to produce frequency modulated Waves in said cavity resonator, and an output circuit coupled to said cavity resonator.

38. High frequency apparatus comprising a cavity resonator having gap, an electron discharge system for producing a flow of electrons across said gap, said discharge system comprising cathode, a single control grid, accelerating and anode electrodes arranged in the order named, circuits for subjecting said electrodes to suitable operating potentials with respect to each other, a circuit connected between said control grid and cathode for varying the electron flow from said cathode and across said gap in a manner so as to cause high frequency excitation of said cavity, a source of modulating voltages connected to said cathode and accelerating electrode, and an output circuit coupled to the space in said cavity resonator to enable the derivation therefrom of modulated high frequency oscillations.

39. Apparatus as defined in claim 38, characterized by the fact that a coupling circuit is provided coupling the space in said cavity to the control grid and the cathode electrodes of said system.

40. Apparatus for producing frequency modulated waves comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said gap, said system comprising cathode, a single control grid, accelerating and anode electrodes arranged in the order named, a two-conductor circuit couplin the space within said cavity to the control grid and cathode of said system, a circuit for suitably polarizing said anode with respect to said cathode, a circuit connected to said accel- 17 crating electrode and cathode for subjecting said accelerating electrode to a variable voltage with respect to said cathode so as to produce frequency modulated Waves in said cavity resonator, and an output circuit coupled to said cavity resonator.

41. Apparatus as defined in claim 40, characterized by the fact that a high frequency parallel tuned circuit is connected between said grid and cathode and being further characterized by the fact that said two-conductor circuit is inductively coupled to said tuned circuit.

42. High frequency apparatus comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said gap whereby said cavity resonator is excited at high frequencies, said discharge system comprising cathode,'a single control grid, accelerating and anode electrodes arranged in the order named, a circuit connected between said control grid and cathode, a transmission line regeneratively coupling said circuit to said resonator, a source of signal modulating voltages, a circuit connecting said source of modulating voltages to said cathodes and another of said electrodes, whereby the transit time of electrons across said gap is varied, and an output circuit coupled to the space in said cavity resonator to enable the derivation therefrom of modulated high frequency oscillations.

43. Apparatus for producing frequency modulated waves comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said gap, said system comprising cathode, a single control grid, accelerating and anode electrodes arranged in the order named, a circuit regeneratively coupling said cavity resonator to the control grid and cathode of said system, a circuit for suitably polarizing said anode with respect to said cathode, and a modulation circuit connected to said cathode and another electrode of said system for varying the transit time of electrons across said gap, whereby frequency modulation of the waves set up in said cavity resonator occurs, and an output circuit coupled to said cavity resonator for transmitting said frequency modulated waves.

44. Apparatus as defined in claim 43, characterized by the fact that a high frequency tuned circuit is connected between said grid and cathode and being further characterized by the fact that said coupling circuit couples said tuned circuit to the space within said cavity.

45. Apparatus for producing modulated waves comprising a cavity resonator having a gap, an electron discharge system for producing a flow of electrons across said gap, said system comprising cathode, a single control grid, acceleratin and anode electrodes arranged in the order named, a source of high frequency oscillations connected to said grid and cathode electrodes, a circuit coupling the space within said cavity to the control grid and cathode of said system, a circuit for suitably polarizing said anode with respect to said cathode, a circuit connected to said accelerating electrode and cathode for subjecting said accelerating electrode to a variable voltage with respect to said cathode so as to produce modulated waves in said cavity resonator and an output circuit coupled to said cavity resonator.

46. Apparatus as defined in claim 45, characterized by the fact that a high frequency tuned circuit is connected between said grid and cathode and being further characterized by the fact that said circuit which couples the space Within said cavity to the control grid and cathode includes a transmission line which is coupled to said tuned circuit.

. FRED H. KROGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,257,795 Gray Oct. 7, 1941 2,280,824 Hansen Apr. 28, 1942 OTHER REFERENCES Journal of Applied Physics, vol. 10, May 1939, pp. 321-327. Copy in Library. 

